Testing a pm dc motor

[Paul Conners]

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

 

[Allan]

On Friday, 6 March 2015 07:37:11 UTC, Paul Conners wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

That's the problem trying to measure motors. If it's ok it's always going to read low ohms, but maybe it should read 3.2ohms (eg) and has shorted turns (eg), how would you ever know? If on the other hand it measured K ohms it would be faulty. An insulation test from windings to armature would be more appropriate. If that's ok give it a spin (I mean apply power).

 

[Baron]

Paul Conners prodded the keyboard with:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult
location to examine visually so i'd like to start with electrical
evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

If it isn't turning, then check that it has actually got voltage
applied to it. You have to consider both the motor and controller !

--
Best Regards:
Baron.

 

[DecadentLinuxUserNumeroUn]

On Fri, 06 Mar 2015 14:50:23 -0500, Michael Black wrote:

On Thu, 5 Mar 2015, Paul Conners wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult
location to examine visually so i'd like to start with electrical
evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.


The faq, http://www.repairfaq.org has some words about the testing of
DC motors, though I'm not sure where.

I think Sam did write something about checking CD player motors, and I'm
sure he gave tips on figuring out whether it was good or bad.

Michael

Not likely that his info is pertinent for 180 volt motors of that size,
when his info is for miniature DC motors.

The motor types likely differ as well.

 

[John Larkin]

On Thu, 5 Mar 2015 23:37:00 -0800, Paul Conners
<pconners98@gUSmail.com> wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

Can you spin the shaft and see how much voltage it generates?

Ohm it to ground, too.


--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Rich.]

On Thu, 5 Mar 2015 23:37:00 -0800, Paul Conners
pconners98@gUSmail.com> wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location
to
examine visually so i'd like to start with electrical evaluation.

Perhaps if we knew in what way the motor was acting up we could better
suggest a course of diagnostics. Like does it make any noise, does it turn
slowly or not at all, is it popping the breaker, etc.

 

[Michael Black]

On Thu, 5 Mar 2015, Paul Conners wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

The faq, http://www.repairfaq.org has some words about the testing of DC
motors, though I'm not sure where.

I think Sam did write something about checking CD player motors, and I'm
sure he gave tips on figuring out whether it was good or bad.

Michael

 

[Tom Miller]

"Allan" <a_r_macdonald@hotmail.com> wrote in message
news:a3e43cf3-3ede-4952-b0f8-fe58fe30ccad@googlegroups.com...
On Friday, 6 March 2015 07:37:11 UTC, Paul Conners wrote:

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location
to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

That's the problem trying to measure motors. If it's ok it's always going to
read low ohms, but maybe it should read 3.2ohms (eg) and has shorted turns
(eg), how would you ever know? If on the other hand it measured K ohms it
would be faulty. An insulation test from windings to armature would be more
appropriate. If that's ok give it a spin (I mean apply power).

+++++++++++++++++++++++++++++++++=

The resistance sounds too low. Can you rotate the armature and re measure at
a different point?

A 180 volt DC 1 hp motor should require around 5 amps or less at full load.
I would expect somewhere around 40-50 ohms when running under full load.

But as others have said, you want to check from the armature to frame
ground. Any resistance might be bad.


Regards

 

[Maynard A. Philbrook Jr.]

In article <0001HW.D11E991C05E771E8B01029BF@news.eternal-september.org>,
pconners98@gUSmail.com says...

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

thanks.

those kind of motors tend to have mechanical issues..

Bearings is common which causes a tight turning shaft
and may cause the armature to move around on the brushes.

Also, a bearing could be completely blown out and the motor
will still make attempts to turn if the brushes are still making
contact.

Another issue is the PM's some times fall off, lose their bond to
the outer shell and come in contact with the rotor.

Then you get the occasion of weak magnets due from too many hours of
running hot, which causes more Arm current and lack of torque but with
higher RPM abilities.

Now and then, the armature windings may short to each other but not to
ground. Most of the time megger meters will not reveal this defect but
usually signs of over heated wire is a good bet.

Also, if you manually spin the motor it can act as a generator..

Disconnect the leads to the motor and see if it turns freely, if so then
you most likely do not have mechanical issue.. Now connect the ARM leads
together from the motor and see if you get heavy drag (Dynamic Braking)
due to energy being generated and short via the A1 and A2 leads. If you
do get a got drag on it, chances are it's of.

When checking the brushes via the DMM, you need to turn the motor very
slowly so that you can account for all the armature bars, you may have a
set of scorched brushes.

Jamie

 

[Tom Miller]

"Paul Conners" <pconners98@gUSmail.com> wrote in message
news:0001HW.D1227BC206CD4457B01029BF@news.eternal-september.org...

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location
to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

Motor out of the equipment. Turning armature slowly, the resistance
reading
between the armature leads varies from a low of 2.3 to high of 10; most
are
around 6-7 ohms. Resistance of each lead to motor frame is minimum 150K up
to
over 1 meg.

What's normal for such a motor?

Thanks.

Open it up and see if it has discolored windings. Does it smell burned? It
would seem to me that the resistance readings indicate compromised winding
insulation.

 

[Paul Conners]

180 vdc, 1 hp, pm motor.

with dmm what should be the first tests? motor is in a difficult location to
examine visually so i'd like to start with electrical evaluation.

it measures 1.2 ohms between the 2 armature leads.

Motor out of the equipment. Turning armature slowly, the resistance reading
between the armature leads varies from a low of 2.3 to high of 10; most are
around 6-7 ohms. Resistance of each lead to motor frame is minimum 150K up to
over 1 meg.

What's normal for such a motor?

Thanks.

 

[Mike]

On Sun, 08 Mar 2015 22:20:50 -0800, Paul Conners wrote:

> Motor out of the equipment. ...

Now you can wind a bit of string round the shaft and pull it to see if it
generates any DC output! Of course if there's another motor you can link
it to with a bit of hose or similar (as a flexible coupling; no water!),
so much the better.

Mike.

 

[Paul Conners]

Now you can wind a bit of string round the shaft and pull it to see if it
generates any DC output! Of course if there's another motor you can link it
to with a bit of hose or similar (as a flexible coupling; no water!), so much

the better.

Mike.

Will check or DC output.

Ah, now that you mention it, this equipment experienced a flood which
probably submerged the motor fully for 48 hours (late last year). Not
operated when submerged (!) but probably some moisture still in it when first
operated after the flood. (2 other equipment suffered damage: a VFD and a
contactor burnt out.)

Thanks.

 

[Paul Conners]

> Will check or DC output.

Will check *for* DC output...

 

[Tom Miller]

"Paul Conners" <pconners98@gUSmail.com> wrote in message
news:0001HW.D122F18906E8DEF3B01029BF@news.eternal-september.org...

Now you can wind a bit of string round the shaft and pull it to see if it
generates any DC output! Of course if there's another motor you can link
it
to with a bit of hose or similar (as a flexible coupling; no water!), so
much

the better.

Mike.

Will check or DC output.

Ah, now that you mention it, this equipment experienced a flood which
probably submerged the motor fully for 48 hours (late last year). Not
operated when submerged (!) but probably some moisture still in it when
first
operated after the flood. (2 other equipment suffered damage: a VFD and a
contactor burnt out.)

Thanks.

That is something that should have been noted up front. You have a bad
motor.

 

[Paul Conners]

> That is something that should have been noted up front. You have a bad motor.

Something killed the motor but didn't affect the measurements discussed here?
What could that be?

 

[Paul Conners]

> That is something that should have been noted up front. You have a bad motor.

Something killed the motor but didn't affect the measurements discussed here?
What could that be?